Projectors (beamers) are regularly used nowadays for optically representing data. A projector of this type projects the data to be represented in the form of individual still and/or moving images onto a projection screen, for example. It is known, in the case of a conventional projector, to generate the required excitation radiation with the aid of a conventional discharge lamp, that is to say for example with the aid of an ultra-high pressure mercury-vapor lamp. LARP (Laser Activated Remote Phosphor) technology has also already been used recently. In this technology, a conversion element which is arranged at a distance from the electromagnetic radiation source and comprises or consists of luminophore is irradiated with excitation radiation, in particular an excitation beam (pump beam, pump laser beam). As an alternative thereto, the conversion element can also be arranged directly on the radiation source. Furthermore, electromagnetic radiation that is not laser radiation can also be used as excitation radiation. By way of example, an LED can be used as radiation source. The excitation radiation of the excitation beam is absorbed by the luminophore and converted into conversion radiation (emission radiation) whose wavelength and thus spectral properties and/or color are determined by the conversion properties of the luminophore. By way of example, in the case of a down-conversion, the excitation radiation of the electromagnetic radiation source is converted by the irradiated luminophore into conversion radiation having longer wavelengths than that of the excitation radiation. By way of example, blue excitation radiation (blue laser light) can thus be converted into red or green conversion radiation (conversion light, illumination light) with the aid of the conversion element. An up-conversion is also known, wherein the excitation radiation of the electromagnetic radiation source is converted by the irradiated luminophore into conversion radiation having shorter wavelengths than that of the excitation radiation.
Furthermore, it is known, in projection applications for image generation, to use liquid crystal devices, for example liquid crystal displays (LCDs) or LCOS (liquid crystal on silicon) components. The liquid crystal devices are illuminated with illumination light and the image representation is effected depending on image data, depending on which the LCDs or LCOS components are driven. For the illumination of the LCDs or LCOS components, polarized illumination light is required for image representation. A radiation source that generates polarized light can be used for generating the polarized illumination light. As an alternative thereto, it is possible to use a radiation source that generates unpolarized light, which is polarized before it impinges on the corresponding liquid crystal device.
The generation of polarized light from unpolarized light requires the use of polarizers, which can lead to high optical losses. In the case of the radiation sources which generate polarized light, for example laser light, and which act directly on the LCDs or LCOS components, no polarization that could lead to the optical losses is required, in principle. However, this may be different with the use of LARP technology, since the wavelength conversion of the excitation light (for example from blue to green) by means of a corresponding luminophore may not be polarization-maintaining and the polarization of the laser light may be canceled during the conversion. The unpolarized conversion radiation generated during the conversion may then be polarized again, as a result of which, however, optical losses may arise.
As an alternative to the LCD- or LCOS-based projectors it is known to use DMD (Digital Micromirror Device)-based projectors, in which a polarization of the light is not necessary.